Optical modules, such as transmitters, typically house optical components hermetically in a box, such as a so-called "14-pin butterfly" housing or package. Generally, such optical modules include a laser configured to emit polarized radiation for communications purposes. Preferably, an optical isolator is disposed within or near the laser so as to suppress optical feedback caused by unwanted radiation reflected or scattered back into the laser. Optical isolators are well known in the art and typically comprise a Faraday rotator disposed between two crossed polarizers. See, for example, S. Makio et al., Electronics and Communications in Japan, Part 2, Vol. 74(2), p. 323 (1991).
Recently developed optical isolators, however, employ a distributed configuration so as to advantageously adjust the optical isolation performance for a given radiation wavelength. See, for example, U.S. Pat. No. 5,737,349, entitled "Optical Isolator and Alignment Method," which is commonly assigned and incorporated herein by reference. In this latter instance, the output polarizer or so-called "analyzer" is disposed within an external retainer that is welded to an opening in an end sidewall of the housing. A lens or window disposed within the opening, in part, hermetically seals the module and couples the light to the exterior of the housing. Alternatively, the analyzer is disposed within the sidewall, such as in a tube.
During assembly, the transmission axis of the output polarizer is rotated so as to maximize the optical isolation, with the polarizer then secured in place by welding the retainer to the housing. Any induced stress caused from such welding, or from any other source, however, can be transmitted to the lens or window so as to induce a birefringence. This stress-induced birefringence is typically the most dominant depolarization mechanism responsible for limiting the achievable optical isolation in such optical modules.
It would therefore be desirable to provide an optical module wherein stress induced in the optical components is substantially eliminated or reduced, particularly for optical modules employing distributed optical isolators.